Precise jet alignment for ink jet printer

ABSTRACT

An ink jet printing system in which vernier jet alignment is achieved by positioning an electrode within close proximity to the continuous stream of ink being emitted by the jet and applying a voltage to the electrode so as to create an asymmetrical force field which has a component perpendicular to the ink stream direction and which affects the trajectory of the ink stream. The vernier jet alignment technique reduces the high cost involved in obtaining similar tolerances mechanically and the complexity of electronic alignment after drop formation, and is suitable for either single or multiple jet printer configurations.

United States Patent 1 Loeiffler et al.

[ Apr. 8, 1975 PRECISE JET ALIGNMENT FOR INK JET PRINTER [75] Inventors:Karl Heinz Loeffler, San Jose; Heinz Hermann Weichardt, Pebble Beach,both of Calif.

[73] Assignee: International Business Machines Corporation, Armonk, NY.

221 Filed: July 2,1973

2! Appl. No.: 376,072

[52] US. Cl. 346/75 [5i] Int. Cl. G0ld 18/00 [58] Field of Search 346/75[56] References Cited UNITED STATES PATENTS 2.600.129 6/l952 Richards346/75 X 3,596,275 7/197] Sweet 346/75 X 3,689,936 9/!972 Dunlavey346/75 X OTHER PUBLICATIONS Meier, .I. H.; Nozzle Adjustments inMultinozzle Ink Jet Printers; IBM Tech. Disc. Bulletin, Vol. 14, No. 10,March 1972, p. 3101. Meier, J. H.; Mechanical X-Y Aiming of Ink JetPrinter Nozzles, IBM Tech. Disc. Bulletin, Vol. I5, No. 5, Oct. 1972, p.1683.

Primary E.raminer.loseph W. Hartary Attorney, Agent, or FirmJohn H.Holcombe [57] ABSTRACT An ink jet printing system in which vernier jetalignment is achieved by positioning an electrode within close proximityto the continuous stream of ink being emitted by the jet and applying avoltage to the electrode so as to create an asymmetrical force fieldwhich has a component perpendicular to the ink stream direction andwhich affects the trajectory of the ink stream. The vernier jetalignment technique reduces the high cost involved in obtaining similartolerances mechanically and the complexity of electronic alignment afterdrop formation, and is suitable for either single or multiple jetprinter configurations.

2 Claims, 2 Drawing Figures FIITENTED PR 81975 BIAS CONTROL EXITATIONSOURCE FIG.

FIG.2

PRECISE JET ALIGNMENT FOR INK JET PRINTER FIELD OF THE INVENTION Thisinvention relates to an ink jet printer system and more particularly toa system which has the capability of vernier jet alignment.

BACKGROUND OF THE INVENTION Various types of non-impact printingprocesses have been developed primarily because this approach offerssuch attractive features such as speed and versatility in printingtechniques. One form of non-impact printing process is known as ink jetprinting and involves the modulation of a stream of fluid ink dropswhich are then recorded on a record medium. Various types of ink jetsystems presently exist. One such system employs a small nozzle to whichconductive fluid ink is delivered under pressure. As the ink exits thenozzle. instabilities due to surface tension forces cause the system tobreak up into a series of drops. This break up is synchronized byvibrating thefluid. which results in uniform drop size and spacing. Acharging means is synchronized with the rate of drop formation whichinduces an electrostatic charge upon each drop as it is formed with thesize of the charge directly related to the input signal voltage. The inkdrops with their respective charges then pass through a constantelectric field created by a pair of deflection plates which aremaintained at a relatively high potential difference. The high electricfield causes the ink drops to deflect according to the charge which theycarry. The ink drops then either impact a record medium which results inprinting or enter an ink sump for return to the ink reservoir. 1

In the manufacture of an ink jet system, whether it be a single jet or amultiple jet system, the amount ofali'gnment of the ink jet is afunction of the expense of the precisionrequired to achieve precisealignment. Since precision mechanical parts becomes more expensive asthe precision is increased. there is a trade-off point at which anyfurther mechanical alignment becomes too expensive. Unfortunately. thistrade-off point often falls short of the desired alignment tolerances.Further precision alignment has been attempted by the addition ofcircuitry in the charge electrode system which adds an additional factorof variance in the charging of the drop based on alignmentconsiderations. The drawback of such a technique is that it results in asingle plane correction capability. Similar techniques which at temptcompensation at points further along the trajectory after drop formationhave been also been em ployed. However, since these compensationtechniques .operate on the individual drops, they must be synchronizedwith the drops adding a further degree of complexity and expense to thealignment process.

OBJECTS OF THE INVENTION Therefore, it is an object of this invention toalign the ink jet in an improved manner.

It is a further object of this invention to align the ink jet prior todrop formation so as to remove any requirementfor synchronization in thealignment.

It is still a further object of this invention to align. the ink jetelectrically prior to drop formation.

It is still a further object of this invention to increase the alignmentcapabilities to more than one plane.

SUMMARY OF THE INVENTION The above objects are accomplished bypositioning a control means such as an electrode within close proximityto the continuous stream of conductive fluid ink after the fluid isemitted from the ink jet nozzle but prior a unilateral or asymmetricalelectric force field which can be adjusted so as to provide precisevernier alignment. The electrode may be placed perpendicularly to thecontinuous stream, resulting in an electric field which exerts a forceonly on the jet without affecting the charges of the drops breaking offfurther down the stream. The applied force results in a velocitycomponent at right angles to the direction of the jet. The electrode isconnected to a control source which may be used to vary the potential ofthe electrode so as to affect the alignment whenever desirable.

The use of the alignment electrode prior to drop formation results in aprinting system alignment technique which may be used on either singleor multiple jet systems, is inexpensive to incorporate into the system,can operate in more than one plane, and provides precise jet alignment.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a multiple ink jetprinting system in which correction electrodes are employed.

FIG. 2 shows in schematic form that area of an ink jet system betweenthe nozzle and the charge electrode where the correction electrode ispositioned for precise alignment.

DETAILED DESCRIPTION FIG. 1 shows a multiple ink jet printing system inwhich correction electrodes are used to attain precise jet alignment.Conductive fluid is delivered under pressure to manifold 10 where itexits by orifices 12 in continuous streams 14. The ink is excited inmanifold 10 by means of piezoelectric crystals 16 mounted on the wall ofmanifold 10 opposite orifices 12. Piezoelectric crystals 16 areconnected to an excitation source 17 which provides a constant frequencyvoltage. The agitation ofthe ink in manifold 10 by piezoelectriccrystals 16 causes the ink streams 14 to break-up into uniform drops 18which are uniformly spaced. Charge electrodes 20 are positioned withinclose proximity to ink streams 14 at the point of break-up. Chargeelectrodes 20 are connected to a signal source (not shown) whichprovides a voltage proportional to an input signal. The voltage suppliedto the charge electrodes 20 are induced upon drops 18 as they pass bycharge electrodes 20. Drops 18 then pass through constant electricfields created by deflection plates 22 and continue towards recordmedium 24. Depending upon the deflection of the ink droplets 18 which inturn is determined by the amount of charge placed on'them by chargeelectrodes 20, ink droplets 18 either impact record medium 24 or enterink sump 26 for recirculation in the system.

The system as described to this point is considered to be within theprior art. It can be seen by referring to FIG. 1 that precise alignmentof the orifices would be an expensive and difficult process. This isespecially true in the multiple jet system where the expense anddifficulty increases with the number ofjets being used. This inventionachieves precise ink jet alignment by means of correction electrodes 28placed in close proximity to continuous streams 14 prior to break-upinto drops 18. As is shown in FIG. 1, correction electrodes 28 areconnected to bias control 30 which simply supplies an adjustablepotential to correction electrodes 28. When correction electrodes 28 arebiased by bias control 30, an electric force field is created which actsupon conductive ink 14. The applied force results in a component atright angles to the direction of continuous stream 14. Thus, theelectric field exerts a force only on the jet without affecting thecharges of the drops 18 which are breaking off further down the streams.While HO. 1 shows correction electrodes 28 affecting continuous streams14 in the vertical direction, correction electrodes 28 would have thecapability of being positioned around continuous streams 14 such thatthe force could be applied in any desired direction. Thus, vernieradjustment is achieved by the use of a unilateral electric force fieldapplied to the liquid jet prior to thejets breaking in the drops. Suchan apparatus is inexpensive, easily implemented and may be applied inany plane. FIG. 2 depicts in schematic form the placement of correctionelectrode 28 relative to continuous stream 14. It should be noted thatwhile correction electrode 28 is shown and described as being placedbetween nozzle plane 32 and charge electrode 20, it is only necessarythat correction electrode 28 be placed within close proximity tocontinuous stream 14 prior to stream 14 breaking up into drops 18. lt isdesirable that correction electrode 28 have a large diameter and beplaced in close proximity to continuous stream 14. This allows a lowervoltage to be placed on correction electrode 28. However, it will berecognized that if correction electrode 28 is placed too close tocontinuous stream 14, ink may strike correction electrode 28. Therefore.there exists a minimum practical distance between correction electrode28 and continuous stream 14. Further, while a large diameter isdesirable for correction electrode 28, the space usually availablebetween nozzle plane 32 and charge electrode is limited and, therefore.limits the diameter size of correction electrode 28.

In operation, ink is delivered under pressure to manifold 16 and exitsthrough orifices 12 in continuous streams 14. Continuous streams 14 passcorrection electrodes 28 which are biased at positive potentials by biascontrol 30. Since the ink is conductive, a dipole effect occurs oncontinuous streams 14 in which the surfaces of conductive streams 14closest to correction electrodes 28 become negative with respect to thesurfaces further away from correction electrode 28. This creates anattractive force between correction electrodes 28 and continuous streams14 causing continuous streams 14 to realign in the directions ofcorrection electrodes 28. This results in continuous streams l4continuing at an angle at as shown in FIG. 2 to its normal projectedflight path 34. The size of a is dependent on the potential supply tocorrection electrodes 28 by bias control which is adjustable. Continuousstreams 14 then reach charge electrodes 20 at which point continuousstreams l4 breakup into drops 18 and receives charges from chargeelectrodes 20 and proceed to pass through the electric fields created bydeflection plates 22. Drops 18 deflect in the fields created bydeflection plates 22 proportional to their charge and pass on to eitherimpact print medium 24 or to enter sump 26 for return to the ink system.

While the invention has been particularly shown and described withreference to a preferred embodiment thereof, it will be understood bythose of skill in the art that various changes in form and detail may bemade without departing from the spirit and scope of the invention. Forexample, while charge electrode 28 has been shown as straight wireelectrode perpendicular to continuous stream 14, it is understood thatvarious shape and configurations of electrodes which will produce anelectric field having a component at right angles to the direction ofcontinuous stream 14 may be employed. Further, the correction techniquedisclosed may be employed with any fluid jet stream which employs aconductive fluid which is emitted in a continuous stream.

We claim: 1. An alignable recording system for precisely recording on arecording medium comprising:

a source of conductive fluid, a nozzle means for ejecting saidconductive fluid in a continuous stream towards said recording medium;excitation means for agitating said conductive fluid prior to ejectionfrom said nozzle means to cause said continuous stream to break up intouniform droplets at a point spaced from said nozzle means; a chargingmeans positioned between said nozzle means and said recording medium andin close proximity to said continuous stream at said point where saidcontinuous stream breaks up into droplets for selectively impartingcharges to said droplets. deflection plates positioned between saidcharging means and said recording medium such that said droplets passthrough the electrostatic fleld created by said deflection plates fordeflecting said charged droplets along one dimension; and a bias controlmeans positioned between said nozzle means and said charging means andin close proximity to said continuous stream prior to said point ofbreakup for creating a constant force field to transversely deflect saidcontinuous stream along a second dimension approximately perpendicularto said one dimension for alignment of said stream. 2. In an ink jetprinter having a pressurized ink manifold means, an ink jet nozzle meansfor directing conductive ink from said manifold means in a continuousink jet stream, excitation means in said manifold for actuating said inkjet to cause said stream to break into uniformly spaced droplets at apredetermined point,

continuous stream at said predetermined point for selectively chargingsaid droplets, deflection plates posi-' tioned subsequent to chargingmeans such that said droplets pass through the field created by saiddeflection plates for deflecting said charged droplets along a firstdimension, and record media means for receiving drops of ink produced bysaid ink jet, in combination therewith,

correction biasing means positioned in close proximity to said ink jetand intermediate said nozzle means and said charging means where the inkjet is still in a continuous stream prior to said predetermined point,for creating a constant force field for deflecting said ink jet streamalong a second dimension perpendicular to the direction of said ink andperpendicular to said one dimension for alignment of said ink jetstream.

1. An alignable recording system for precisely recording on a recordingmedium comprising: a source of conductive fluid, a nozzle means forejecting said conductive fluid in a continuous stream towards saidrecording medium; excitation means for agitating said conductive fluidprior to ejection from said nozzle means to cause said continuous streamto break up into uniform droplets at a point spaced from said nozzlemeans; a charging means positioned between said nozzle means and saidrecording medium and in close proximity to said continuous stream atsaid point where said continuous stream breaks up into droplets forselectively imparting charges to said droplets, deflection platespositioned between said charging means and said recording medium suchthat said droplets pass through the electrostatic field created by saiddeflection plates for deflecting said charged droplets along onedimension; and a bias control means positioned between said nozzle meansand said charging means and in close proximity to said continuous streamprior to said point of breakup for creating a constant force field totransversely deflect said continuous stream along a second dimensionapproximately perpendicular to said one dimension for alignment of saidstream.
 2. In an ink jet printer having a pressurized ink manifoldmeans, an ink jet nozzle means for directing conductive ink from saidmanifold means in a continuous ink jet stream, excitation means in saidmanifold for actuating said ink jet to cause said stream to break intouniformly spaced droplets at a predetermined point, charging meanspositioned in close proximity to said continuous stream at saidpredetermined point for selectively charging said droplets, deflectionplates positioned subsequent to charging means such that said dropletspass through the field created by said deflection plates for deflectingsaid charged droplets along a first dimension, and record media meansfor receiving drops of ink produced by said ink jet, in combinationtherewith, correction biasing means positioned in close proximity tosaid ink jet and intermediate said nozzle means and said charging meanswhere the ink jet is still in a continuous stream prior to saidpredetermined point, for creating a constant force field for deflectingsaid ink jet stream along a second dimension perpendicular to thedirection of said ink and perpendicular to said one dimension foralignment of said ink jet stream.